1. Field of the Invention
This invention relates to a process for producing a novel lithium niobate single crystal. More particularly, this invention relates to a process for producing a novel lithium niobate single crystal in which a compositional evaluation of crystals based on Curie point can be accurately conducted, and, as a result, a high-quality lithium niobate having a homogeneous composition can be produced with good reproducibility, whereby the yield at the time of producing an optical device can be improved.
2. Prior Art
As one of the processes for determining the composition of lithium niobate (LiNbO.sub.3, generally abbreviated as LN) used for the production of optical devices and the like, measurement of Curie points (Tc) has been performed. It has been known that this temperature varies with the ratio of lithium (Li) to niobium (Nb) of the crystals and that the Curie point is raised with a great amount of Li. In order to determine the compositional change of lithium niobate single crystals by utilizing the above properties, the evaluation of the Curie point has been conducted. It is important to eliminate all other factors that cause a variation in the Curie point. Even if a difference in the Curie point is observed among samples, it cannot always be said that the difference is due to the compositional change. Consequently an accurate evaluation concerning the composition of the crystals cannot be obtained. We have investigated the factors that vary the Curie point and, as a result, found that there is a factor having an effect on the Curie point depending upon the type of impurities contained in lithium niobate and that factor becomes a great obstacle in the investigation of compositional change due to the Curie point.